1. Field of the Invention
The present invention pertains to two piece, two component HCR silicone addition-curable elastomers.
2. Background Art
Addition-curable silicone elastomers find widespread use as gasketing materials, casting resins, caulks, sealants, and coatings. These elastomers contain an organopolysiloxane bearing ethylenic or ethylynic (“aliphatic”) unsaturation and a further organopolysiloxane or silane bearing silicon bonded hydrogen (Si—H) functionality. The elastomers cure by hydrosilylation of the organopolysiloxane containing unsaturated groups with Si—H groups, a reaction catalyzed by a hydrosilylation catalyst, preferably platinum or platinum compounds or complexes.
Both one component and two component formulations are known. One component formulations contain both reactive components as well as the hydrosilylation catalyst in the same composition. To prevent premature cure, catalysts which are effective only at elevated temperatures and/or inhibitors which inhibit the hydrosilylation reaction must be present. However, even so, shelf life is often limited, and storage conditions must be carefully regulated. Compositions of this type, which may range from viscous liquids to pastes are commercially available, one example being RTV-1 caulks and sealants.
To avoid the limited storage stability or “pot life” of one component compositions, two component compositions are widely used industrially. In these compositions, e.g. RTV-2 elastomers, the catalyst is compounded either with the ethylenically unsaturated organopolysiloxane or with the Si—H functional components, but not with both at the same time. Prior to use, the two separate compositions are homogeneously mixed and used immediately.
Two component systems are practically limited to liquid components, which allow the compounds to be mixed employing equipment commonly available, such as static mixers, mechanical mixers, and the like. Unfortunately, the liquid nature of such products prevents their use in many applications in which pressure is to be applied prior to full cure being obtained. Under these conditions, the composition, even when quite viscous, may flow away from the area in which the elastomer is desired. It would be desirable to provide a solid elastomer composition which eliminates the above disadvantages, yet has extended or even unlimited storage life.